Method of preparing alpha amides

ABSTRACT

COMPRISING ESTERIFYING THE (5) CARBOXYL GROUP OF GLUTAMIC ACID WITH BENZYL ALCOHOL, BENZOYLATING THE AMINO GROUP OF THE ESTER THUS OBTAINED, AMIDATING THE (1) CARBOXYL GROUP OF THE BENZOYLATED ESTER, AND DEBENZYLATING THE AMIDATED BENZOYLATED ESTER. METHOD OF PREPARING AN ALPHA-AMIDE OF THE GENERAL FORMULA:   C6H5-CO-NH-CH(-CO-R)-CH2-CH2-COOH

United States Patent 3,739 ,013 METHOD OF PREPARING ALPHA AMIDESGiampaolo Picciola and Luigi Rovati, Milan, Italy, asgigilors to RottaResearch Laboratorium S.p.A., Milan,

ta y No Drawing. Filed Sept. 23, 1970, Ser. No. 74,926 Claims priority,application Italy, Oct. 13, 1969, 53,660/ 69 Int. Cl. C07c 103/30 U.S.Cl. 260-471 R 8 Claims ABSTRACT OF THE DISCLOSURE Method of preparing analpha-amide of the general formula:

('Y) C O OH 2 (2) (L'HNH- C O@ JO-R (I) comprising esterifying the (5)carboxyl group of glutamic acid with benzyl alcohol, benzoylating theamino group of the ester thus obtained, amidatin-g the (l) carboxylgroup of the benzoylated ester, and debenzylating the amidatedbenzoylated ester.

SUMMARY OF THE INVENTION This invention relates to particular amides ofN-bcnzoyl-glutamic acid having the general formula:

C POHr-C H OHzGH CH or a (p-carboalkoxy)-phenylamino group:

where R is an alkyl group having from 1 to 6 carbon atoms.

The Formula I also indicates the nomenclature for identifying thevarious carbon atoms in the amino-acid chain.

These particular amides, along with their gamma isomers, form part of aclass of compounds covered by previous patents taken out by the presentapplicants (of. French Patent 5853 M, for example), in which' adescription was also given of methods of obtaining compounds in thatclass from glutamic acid, and consideration was given to the possibilityof separating the alpha and gamma isomers or indeed of obtainingselectively one or other of those isomers.

The present invention arises from the following two considerations:

(a) The pharmacological activity (as a gastric antisecretive) oi FormulaI amides, in which, that is to say, the substituent R occupies position(1), is greater than that of the respective gamma isomers, in which thesubstituent occupies the position (5).

(b) None of the processes described previously offered the possibilityof forming the alpha isomer alone, on an 3,739,013 Patented June 12,1973 industrially acceptable basis, taking also into account theconfiguration (L, DL or D) of the original glutamic acid.

The purpose of the present invention is therefore to provide ahigh-yield process, with retention of configuration (that is to saywithout changing the configuration of the original glutamic acid, whichmay equally Well be L, DL or D) and selective for amidation in the alphaposition, enabling amides having the Formula I to be obtained incommercially advantageous conditions.

DETAILED DESCRIPTION OF THE INVENTION The invention process may berepresented in diagram form as follows:

The glutamic acid is esterified with benzyl alcohol in the presence of astrong mineral acid such as, for example, sulphuric, phosphoric,hydrochloric, hydrobromic, hydriodic or hydrofluoric acid; sulphuricacid should be used for preference, at a temperature of between 0 C. and25 0., possibly but not necessarily in the presence of an inert organicsolvent, such as ether or benzene.

The ester so obtained is benzoylated with benzoyl chloride dissolved ina suitable water-miscible organic solvent such as dioxane ortetrahydrofuran in an aqueous medium and in the presence of a protonacceptor such as, for instance, sodium carbonate, at a temperaturevarying between -2 C. and +15 C. The proton acceptor must benon-hydrolysing in relation to benzyl esters, so as not to restore theinitial glutamic acid. It is thus necessary to avoid using strong basessuch as caustic soda, but it is possible to use sodium carbonate, forexample, or magnesium oxide.

The benzyl ester of N-benzoyl glutamic acid thus obtained is dissolvedin an organic solvent such as tetrahydrofuran, dioxane or methylenechloride and amidated at the free carboxyl group with an amine R-H (Rhaving the significance already explained), in the presence ofdicyclohexylcarbodiimide or N,N'-carbonyldiimidazol as condensing agent,at a temperature between 10 C. and +25 c.

The amide is then debenzylated catalytically in the presence of acatalyst such as palladium on carbon or palladium chloride, in asolution of methanol, ethanol, propanol or isopropanolpreferablymethanol-at room temperature, in a stream of hydrogen, until theevolution of carbon dioxide ends. The reaction can be accelerated by thepresence of acetic acid to the extent of 5% to 10% related to thesolvent employed. The reaction mixture is filtered and the solventevaporated in vacuo. The residue is dissolved in an organic solvent suchas, for example, ethyl acetate; ethyl ether, benzene or chloroform andextracted with an alkali metal hydrate, carbonate or bicarbonate.Acidification produces the desired amide of N- benzoyl glutarnic acid.

EXAMPLE 1 Part 1: Preparation of the q-benzyl ester of L-glutamic acid(III) To 1,000 ml. of anhydrous ethyl ether is added 100 ml. of 98%sulphuric acid at C., agitation being applied, followed by 1,000 ml. ofbenzyl alcohol. The ether is distilled in vacuo and 147.13 g. (1 mol)(M.W. 147.13) of L-glutamic acid is added a little at a time.

The solution so obtained is left under agitation for 24 hours at 20 C.;then cooled to 0 C. and 2,000 ml. of 95% ethanol and 500 ml. of pyridineare added.

The resultant product soon begins to crystallise. This is allowed tostand for 24 hours to 0 C. and then filtered. This produces 211 g. of'y-benzyl-L-glutamate (M.W. 237.20) having a melting point of 175 176C.; [a] =+19.8 (c.=6 in acetic acid). Yield 89%.

Part 2: Preparation of the acid of N-benzoyl-L-glutamic acid 'y-benzylester (IV) Of the ester obtained in part 1, 118.5 g. (0.5 mol) issuspended in 800 ml. of water. In this suspension, 53 g. (0.5 mol) ofsodium carbonate is dissolved, this being followed by the addition, in 2hours and at 0 C., of 58.2 ml. (0.5 mol) of benzoyl chloride dissolvedin 300 ml. of anhydrous tetrahydrofuran.

The addition having been completed, a further 3 g. of sodium carbonateis added and the whole is left for 20 hours under agitation of 10 C.Extraction is carried out with 500 cc. of ether, the pH value isadjusted to 2 and extraction is then carried out in turn with 4 portionsof 400 ml. of ethyl acetate; this extract is washed with salt water anddehydrated with magnesium sulphate and the ethyl acetate is distilled invacuo. The residue is crystallized from benzene. This produces 155 g. ofester (IV) (M.W. 341.2) having a melting point of 128129 C.; [a] -8.2(c.=4 in 95% ethanol).

Part 3: Preparation of the a-(di-n-propyDamide of N-benzoyl-L-glutamicacid y-benzyl ester To a solution of 34.1 g. (0.1 mol) of ester (IV) in500 ml. of tetrahydrofuran, maintained at 5 C., are added 10.12 g. (0.1mol) of di-n-propylamine and 20.63 g. (0.1 mol) of dicyclohexylcarbodiimide. After agitation for 16 hours this is filtered andevaporated to dryness. The residue is dissolved in ethyl acetate, washedfirst with aqueous bicarbonate, then with 2 N hydrochloric acid andfinally with water, dehydrated and evaporated to dryness. This produces40.5 g. of a semi-solid glutinous substance, which is passed in thatstate to the next stage. Yield 95 Part 4: Preparation of thea-(di-n-propyDamide of N-benzoyl-L-glutamic acid Of the substanceobtained in part 3, 40.5 g. (0.095 mol) is dissolved in 400 ml. ofmethanol, 2 g. of palladiated carbon is added and hydrogenation iscarried out at ambient temperature in a stream of hydrogen for 6 hours.Filtration follows and the methanol is distilled in vacuo. The residueis dissolved in ethyl acetate, ex-- tracted with aqueous sodiumcarbonate and precipitated With hydrochloric acid. Crystallisation takesplace with chloroform. This produces 29.2 g. (M.W. 334.40). Yield 91%;[oz] =41.6 (c.=1.2 in DMF); overall yield (referred to the initialglutamic acid): 70:00%.

The substance is chromatographically pure.

On unactivated DC platesFertigplatten Kieselgel F of Merck-the resultis:

4 Rf 0.5 in n-butanol saturated with water; Rf 0.87 n-butanol-aceticacid-H O (5 :2: 1) A Wood lamp of 254 m wavelength is used as detector.

The fact that this is an a-amide is confirmed by the method of King andMcMillan, J. Am. Chem. Soc. 74, (1952), 5 202, no carbon dioxide beingevolved upon heating in acetic anhydride and pyridine, contrary to whathappens in the case of v-amides.

EXAMPLE 2 Part 1: Preparation of the benzyl ester of DL-glutamic acid T01,000 ml. of anhydrous ethyl ether are added, agitation being applied,first 100 ml. of 98% sulphuric aicd at 0 C. and then 1,000 ml. of benzylalcohol. The ether is distilled in vacuo and 147.13 g. (1 mol) ofDL-glutamic acid is added a little at a time.

The resultant solution is left under agitation for 24 hours at 22 C.,after which it is cooled to 0 C. and 2,000 ml. of ethanol and 500 ml. ofpyridine are added.

The product soon begins to crystallise. It is left to stand for 24 hoursat 0 C. and filtered, 214 g. of v-DL-benzyl glutamate (M.W. 237.2)having a melting point of 162- 163 C. being obtained. Yield 90.2%.

Part 2: Preparation of N-benzoyl-DL-glutamic acid 'y-benzyl ester Of theester obtained in part 1 of this example, 118.5 g. (0.5 mol) issuspended in 800 ml. of water. In this suspension, 53 g. (0.5 mol) ofsodium carbonate is dissolved, this being followed by the addition, in 2hours at 0 C., of 58.2 ml. (0.5 mol) of benzoyl chloride dissolved in300 ml. of anhydrous tetrahydrofuran.

The addition having been completed, a further 3 g. of sodium carbonateis added and the whole is left for 20 hours under agitation at 10 C.Extraction is carried out with 500 cc. of ether, the pH value isadjusted to 2 and extraction is then carried out with 4 portions of 400ml. of ethyl acetate; this extract is washed with salt water anddehydrated with magnesium sulphate and the ethyl acetate is distilled invacuo. The residue is crystallised with benzene. This produces 154 g. ofthe benzioyl ester (M.W. 341.2). Melting point 116117 C. Yield 91.0%.

Part 3: Preparation of the a-(di-n-propyDamide of N-benzoyl-DL-glutamicacid 'y-benzyl ester To a solution of 34.1 g. (0.1 mol) of the esterobtained in part 2 in 5 00 ml. of tetrahydrofuran, maintained at 5 C.,are added 10.12 g. (0.1 mol) of di-n-propylamine and 20.63 g. (0.1 mol)of dicyclohexyl carbodiimide. After agitation for 16 hours, this isfiltered and evaporated to dryness. The residue is dissolved in ethylacetate, Washed first with aqueous bicarbonate, then with 2 Nhydrochloric acid and finally with water, dehydrated and evaporated todryness. This produces 41 g. of a semisolid glutinous substance (M.W.424.2), which is passed in that state to the next stage. Yield 96.5%.

Part 4: Preparation of the u-(di-n-propyDamide of N-benzoyl-DL-glutamicacid Of the substance obtained in part 3 of this example, 41 g. (0.0965mol) is dissolved in 400 ml. of methanol, 2 g. of 10% palladiated carbonis added and hydrogenation is carried out at ambient temperature for 6hours in a stream of hydrogen. Filtration follows and the methanol isdistilled in vacuo. The residue is dissolved in ethyl acetate, extractedwith aqueous sodium carbonate and precipitated with hydrochloric acid.Crystallisation takes place with chloroform. This produces 30.4 g. (M.W.334.4); melting point 143 -144 C. Yield 94.2%. Overall yield 74.1%.

- This product too, when subjected to the tests referred to in Example1, part 4, is shown to be a chromatographically pure a-amide.

Example 3 Part 1: Preparation of the 'y-benzyl ester of D-glutamic acidTo 1,000 ml. of anhydrous ethyl ether are added, agitation beingapplied, first 100 ml. of 98% sulphuric acid at C. and then 1,000 ml. ofbenzyl alcohol. The ether is distilled in vacuo and 147.13 g. (1 mol) ofD-glutamic acid is added a little at a time.

The resultant solution is left agitation for 24 hours at 22 C., afterwhich it is cooled to 0 C. and 2,000 ml. of 95 ethanol and 500 ml. ofpyridine are added.

The product soon begins to crystallise. It is left to stand for 24 hoursat 0 C. and filtered. This produces 205 g. of y-D-benzyl glutamate (M.W.237.2) having a melting point of 267268 C. [a] =28..1 (c.=9.8 in HCl 1N). Yield 86.5%.

Part 2: Preparation of N-benzoyl-D- glutamic acid 'y-benzyl ester Of the'y-benzyl ester obtained in Part 1 of this example, 118.5 g. (0.5 mol)is suspended in 800 ml. of water. In this suspension, 53 g. (0.5 mol) ofsodium carbonate is dissolved, this being followed by the addition, in 2hours at 0 C., of 58.2 ml. (0.5 mol) of benzoyl chloride dissolved in300 ml. of anhydrous teerahydrofuran.

The addition having been completed, a further 3 g. of sodium carbonateis added and the whole is left for 20 hours under agitation at 10 C.Extraction is carried out with 500 cc. of ether, the pH value isadjusted to 2 and extraction is then carried out with 4 portions of 400ml. of ethyl acetate; this extract is Washed with salt water anddehydrated with magnesium sulphate and the ethyl acetate is distilled invacuo. The residue is crystallised with benzene. This produces 153 g. ofbenzoyl ester (M.W. 341.2). Yield 90.0%. Melting point 134135 C.;

(c.=4.3 in 95% ethanol).

Part 3: Preparation of the a-(di-n-propyl) amide of N-benzoyl-D-glutamicacid 'y-benzyl ester To a solution of 34.1 g. (0.1 mol) of the ester obtained in part 2 in 500 ml. of tetrahydrofuran, maintained at 5 C., areadded 10.12 g. (0.1 mol) of di-n-propylamine and 20.63 g. (0.1 mol) ofdicyclohexyl carbodiimide. After agitation for 16 hours, this isfiltered and evaporated to dryness. The residue is dissolved in ethylacetate, washed first with aqueous bicarbonate, then with 2 Nhydrochloric acid and finally with water, dehydrated and evaporated todryness. This produces 39.2 g. of a semi-solid glutinous substance (M.W.424.2), which is passed in that state to the next stage. Yield 92.4%.

Part 4: Preparation of the ot-(di-n-propl) amide of N-benzoyl-D-glutamic acid Of the substance obtained in Part 3 of thisexample, 39 g. (0.0924 mol) is dissolved in 400 ml. of methanol, 2 g. ofpalladiated carbon is added and hydrogenation is carried out at ambienttemperature for 6 hours in a stream of hydrogen. Filtration follows andthe methanol is distilled in vacuo from the filtrate. The residue isdissolved in ethyl acetate, extracted with aqueous sodium carbonate andprecipitated with hydrochloric acid. Crystallisation takes place withchloroform. This produces 27 g. (M.W.

334.40). Yield 87.8%. Overall yield 64.5%. Melting point 115-116 C.; [m]=+7.9 (c.-=1.9 in DMF').

This product too, when subjected to the tests referred to in Example 1,part 4, is shown to be a chromatographically pure ot-amide.

6 EXAMPLE 4 Parts 1 and 2 of this example are the same as Parts 1 and 2of Example 1.

Part 3: Preparation of the a-(p-carbethoxy)-phenylamide ofN-benzoyl-L-glutamic acid 'y-benzyl ester To a solution of 34.1 g. (0.1mol) of the ester obtained in Part 2 of Example 1 in 500 ml. oftetrahydrofuran, maintained at 5 C., are added 16.51 g. (0.1 mol) ofethyl p-amino benzoate and 20.63 g. (0.1 mol) of dicyclohexylcarbodiimide.

After agitation for 16 hours, this is filtered and the filtrate isevaporated to dryness. The residue, dissolved in ethyl acetate, iswashed first in aqueous sodium bicarbonate, then in hydrochloric acidand finally in water, dehydrated and evaporated to dryness. Thisproduces 45.3 g. of a semi-solid glutinous substance (M.W. 488.1), whichis passed in that state to the next stage. Yield 92.7%.

Part 4: Preparation of the a-(p-carbethoxy)phenylamide ofN-benzoyl-L-glutamic acid Of the substance obtained in Part 3 of thisexample, 45.3 g. (0.0927 mol) is dissolved in 400 ml. of methanol, 2 g.of 10% palladiated carbon is added and the hydrogenation is carried outat ambient temperature for 6 hours in a stream of hydrogen. The methanolis filtered from the catalyst and distilled from the filtrate in vacuo.

The residue is dissolved in ethyl acetate, extracted with sodiumcarbonate and precipitated with hydrochloric acid. crystallisation takesplace with chloroform. This produces 33.4 g. (M.W. 398.4). Melting point215217 C. [a] =7 (c.=1.3 in DMF). Yield Overall yield 67.6%.

The product consists of chromotographically pure OL- amide; onunactivated DC plates-Fertigplatten Kieselgel F of Merck-the result is:

Rf=0.61 in n-butanol saturated with water; Rf=0.90 in n-butanol-aceticacid-H O (5:2: 1); Rf=0.60 in isoamyl alcohol-acetone H O (5:2: 1).

EXAMPLE 5 Parts 1 and 2 of this example are the same as Parts 1 and 2 ofExample 1.

Part 3: Preparation of the a-(p-carbethoxy-phenylamide ofN-benzoyl-DL-glutamic acid 'y-benzyl ester To a solution of 34.1 g. (0.1mol) of the ester obtained in Part 2 of Example 2 in 500 ml. oftetrahydrofuran, maintained at 5 C., are added 16.51 g. (0.1 mol) ofethyl-p-amino benzoate and 20.63 g. (0.1 mol) ofdicyclohexylcarbodiimide.

After agitation for 16 hours, this is filtered and the filtrate isevaporated to dryness. The residue, dissolved in ethyl acetate, iswashed with sodium bicarbonate, then with water, 2 N hydrochloric acidand water, dehydrated and evaporated to dryness. This produces 461 g. ofa semisolid glutinous substance (M.W. 488.1), which is passed in thatstate to the next stage. Yield 94.4%.

Part 4: Preparation of the a- (p-carbethoxy)-phenylamide ofN-benzoyl-DL-glutamic acid Of the substance obtained in Part 3 of thisexample, 46.1 g. (0.0944 mol) is dissolved in 400 ml. of methanol, 1.5g. of 10% palladiated carbon is added and hydrogenation is carried outat ambient temperature for 6 hours in a stream of hydrogen. The methanolis filtered out of the catalyst and distilled in vacuo.

The residue is dissolved in ethyl acetate, extracted with aqueous sodiumcarbonate and precipitated with hydrochloric acid. Crystallisation takesplace with chloroform.

This produces 33.8 g. (M.W. 398.402). Yield 84.9%. Melting point 208-209 C. Overall yield 65.4%.

This substance too, when subjected to the tests referred to in Example1, Part 4, is shown to be a chromatographically pure a-amide.

What we claim is: 1. A method for preparing an alpha-amide of thewherein R is a member selected from the group consisting of adi-n-propylamino group and a (p-carboalkoxy)- phenylamino group NHC HCOOR, wherein R represents an alkyl group of from 1 to 6 carbon atoms,

which comprises the following steps:

(1) esterifying glutamic acid in the (5) position by reacting saidglutamic acid with benzyl alcohol at a temperature of from 0 C. to 25 C.in the presence of a strong mineral acid,

(2) benzoylating the amino group of the thus obtained ester by reactingthe latter at 2 C. to +15 C. with benzoyl chloride in an aqueous organicinert solvent in the presence of a proton acceptor,

(3) amidating the (1) carboxyl group of the benozylated ester byreacting the latter at 10 C. to l+25 C. with an amine corresponding tothe substituent R in an organic solvent in the presence of a condensingagent, and

(4) debenzylating the amidated ester in an alcoholic solvent bymolecular hydrogenation in the presence 30 of a hydrogenation catalyst.

2. The method of claim 1, wherein said strong mineral acid is sulfuricacid.

3. The method of claim 1, wherein the benzoylation reaction solvent is amember selected from the group consisting of dioxane or tetrahydrofuran.

4. The method of claim 1, wherein said organic inert solvent is a memberselected from the group consisting of dioxane, tetrahydrofuran andmethylene chloride.

5. The method of claim 1, wherein said condensing agent is a memberselected from the group consisting of dicyclohexylcarbodiimide andN,N'-carbonyldiimidazole.

6. The method of claim 1, wherein said proton acceptor is a memberselected from the group consisting of sodium carbonate and magnesiumoxide.

7. The method of claim 1, wherein said alcholic solvent is a memberselected from the group consisting of methanol, ethanol, propanol, andisopropanol.

8. The method of claim 1, wherein said catalyst is a member selectedfrom the group consisting of palladium on a carbon support or palladiumchloride.

References Cited UNITED STATES PATENTS 3,551,419 12/1970 Giorgio et al.2605l8 R LORRAINE A. WEINBERGER, Primary Examiner L. A. THAXTON,Assistant Examiner U.S. Cl. X.R. 260-618 R

